Circuit designers, as a general goal, tend to prefer designs that improve signal-to-noise ratios for audio circuits, radios, wired communication devices, data transmission systems, etc. Generally, two basic approaches for improving signal-to-noise ratios include utilizing communication pathways that are less lossy or have lower noise or, alternatively, by increasing the gain of a gain stage. In some wireless communication systems, such as code division multiple access systems, however, there is a constant feedback processing system to minimize signal power levels while maintaining certain signal-to-noise ratios to reduce the possibility of interfering with other signals.
Sometimes, the solution of increasing the gain is more difficult to realize. For example, a conflicting goal of portable systems is to maximize battery life by minimizing power consumption. Additionally, with the gains in device scaling that are being realized, supply voltages are decreasing thereby leaving less headroom to increase a gain level to improve a signal-to-noise ratio. Generally, decreasing the supply voltage and its associated power tends to decrease signal-to-noise ratios and the dynamic range of a signal or system operation.
More specifically some integrated circuit designs now utilize a supply voltage that is approximately equal to 3.3 volts. Prior integrated circuits, in contrast, utilized a supply that was equal to or greater than 5 volts. These particular trends are contrary to certain design goals such as goals to improve the performance of digital-to-analog converters. In the field of audio systems, signal-to-noise ratios and dynamic range of more than 100 decibels (dB) are often required to achieve the desired system performance. A digital-to-analog converter is used widely in the field of audio systems and is an essential circuit. The increasing miniaturization due to advancements in semiconductor processes continues to drive down supply voltage levels as well as the output range of an analog signal. Furthermore, the signal-to-noise ratios and dynamic range of the digital-to-analog converters will tend to decrease. Accordingly, there is a need to maintain or increase signal-to-noise ratios in the face of such trends.
The use of the same reference symbols in different drawings indicates similar or identical items. Unless otherwise noted, the word “coupled” and its associated verb forms include both direct connection and indirect electrical connection by means known in the art, and unless otherwise noted any description of direct connection implies alternate embodiments using suitable forms of indirect electrical connection as well.